1. Field of Invention
The present invention relates to an arrangement for optical measuring of volatile impurities in contaminated medium such as water.
2. Information Disclosure Statement
The determination of impurities in water (the analytes) by infrared spectroscopy is handicapped by the strong continuous absorption of water in the whole infrared range. U.S. Pat. No. 5,059,396 issued to Opitz et. al. in 1991 teaches an arrangement for optically measuring the concentration of substances in which a measuring space is provided of a material which is selectively permeable for substances to be measured and transparent for a measuring radiation and which is in operative connection with an object to be measured and through which the measuring radiation is transmitted. Opitz teaches the application of a hydrophobic extracting membrane as a measuring space at the surface of an internal reflection element, e.g. an optical fiber or an attenuated total reflection (ATR) crystal. Such an arrangement has the advantage that hydrophobic analytes are extracted into and enriched in the extracting membrane by factors between 10 and 100,000 while water is excluded. The infrared absorption of the substance in the extracting membrane is then measured by the so-called evanescent wave which emerges into the membrane under the condition of total reflection. Thus, continuous determinations are possible. The limit of detection, however, is still too high for many applications. Also, the extracting membrane may be destroyed by material contaminations, especially if the analyte to be measured is contained in waste water. The present application removes these difficulties.
The objectives of the invention are as follows: 1. To significantly reduce the detection limit of volatile impurities in a contaminated medium over the prior art. 2. To increase efficiency and decrease cost as the distillation process of the present invention protects against mechanical wear of the extracting membrane by excluding the abrasive components of the contaminated medium from the membrane. 3. To increase efficiency and decrease cost as the distillation process of the present invention reduces the chemical wear of the membrane by reducing its temperature. 4. To teach the use of alternatives to standard spectroscopy for measurement of analytes in a contaminated medium.